Systems heretofore developed for electronically identifying separate animate or inanimate objects in a group of objects, particularly those systems designed to distinguish between animals in a herd for the purpose of controlling the feed dispensed to the animals, can generally be divided into one of two classes. Systems in the first class carry out the identification process on a gross level only, tagging certain objects with an electronic distinguishing marker and then simply sorting all of the objects according to whether they have or have not been tagged. For example, where certain animals in a herd are selected to receive feed supplements, an electronic distinguishing marker which activates a switching circuit connected to control delivery of the feed supplement to a feeding station is attached to the selected animal. Such electronic distinguishing markers may take many forms, including devices which disturb the magnetic field surrounding a magnetic switching circuit, as disclosed in U.S. Pat. No. 4,162,683 issued to Brooks and U.S. Pat. No. 4,188,912 issued to Smalley; and devices which damp, absorb or otherwise disturb the RF field generated by a RF switching circuit, as disclosed in U.S. Pat. No. 3,465,724 issued to Broadbent, U.S. Pat. No. 3,541,995 issued to Fathauer and U.S. Pat. No. 3,557,757 issued to Brooks.
Systems in the second class provide a means for identifying animate or inanimate objects in a true sense. That is, each animate or inanimate object in a group of objects is tagged with an electronic marker having a characteristic uniquely associated with that object. The electronic marker or identity tag is subsequently "read" via suitable electronic circuitry to obtain the object identity, and the object identity so obtained is used to initiate various control or monitoring sequences. One important application for systems of the second class involves the identification of animals and the dispensing of feed on the basis of the identified animal's individual feed requirements.
Some prior art animal feeding systems employ identity tags having passive RF circuits similar to the RF circuits of the aforementioned Broadbent and Brooks patent, wherein RF energy is absorbed by a detector at several predetermined frequencies uniquely arranged to provide a means for identifying the animals. U.S. Pat. No. 3,516,575 issued to Moffitt and U.S. Pat. No. 3,557,758 issued to Lack disclose passive RF energy absorbing type identity tags. Other prior art animal feeding systems employ identity tags having active RF circuits which radiate RF energy at discrete frequencies to provide a means for identifying the animals. These discrete frequencies are received by a plurality of receiving circuits mounted at or near the animal feeding station. The latter type of active RF identity tag system is disclosed in U.S. Pat. No. 3,180,321 issued to Aldinger.
Frequency-dependent animal identification processes such as those illustrated in the Broadbent, Moffitt and Lack patents are entirely adequate for many applications. Where digital control means are utilized to control the feed delivery operation, however, frequency-dependent systems must be properly interfaced with the digital controller before the identification process can be completed. This interface generally requires an extra analog to digital conversion step in the frequency-dependent signal receiving apparatus, with an attendant increase in circuit complexity and cost. It would be of obvious advantage if the identifier signal radiated from the identity tag were already in digital form.
Perhaps the simplest manner of digital identification involves a simple count. An animal is assigned an identification number, an identity tag having a counter programmed to supply the predetermined number or count is attached to the animal, and whenever a receiver in the vicinity of the animal detects the predetermined count, the animal is identified. U.S. Pat. No. 3,929,277 issued to Byrne et al and U.S. Pat. No. 4,129,855 issued to Rodrian both disclose counting-type identity tags. In the Byrne et al system, a series of RF pulses corresponding in number to a predetermined count are generated by an identity tag counter and transmitted to a receiver for counting. In the Rodrian system, the identity tag counter counts to a predetermined value and then merely transmits a reset pulse to stop the count in a synchronized counter connected to the system transceiver.
Although animal identification signals developed by counting-type identity tags are more conveniently interfaced with digital control means than those developed by frequency-dependent identity tags, if the number of animals to be identified is quite large, it becomes somewhat cumbersome to actually count RF identification pulses. It would thus be even more advantageous to generate an animal identifier signal in compact, coded form for transmission to a digital receiver/decoder. Standard integrated circuit technology could be employed to construct suitable code generators and receiver/decoders at low cost and with reduced size. Further economies of cost and size could be realized by eliminating the need for a separate identity tag power supply in favor of a simple energy absorbing circuit in the identity tag, into which RF energy could be coupled to provide a ready source of power. The ease and convenience of transmitting binary coded identifier signals from an electronic identity tag would render the tag fully compatible with most digital computer configurations, in turn increasing the range of control, monitoring and diagnostic functions available to an animal feeding and monitoring system.